Sonnet powerpc.library currently does not support A1200 Mediators. I believe the developer (Hedeon on EAB) has had some measure of success getting Sonnet and Rapsody working on the A1200 but it is not as developed at the A3000/A4000 solutions. So at the moment, no it does not work with the A1200.
More information here on the sonnet wiki
https://github.com/Sakura-IT/SonnetAmiga/wikiAnd on the massive EAB thread
http://eab.abime.net/showthread.php?t=76633Sonnet does not currently work with OS4. That might change in the future but I don't believe it's currently being worked on by the team (could be wrong about this).
Sonnet works alongside most (if not all) accelerator cards for big box amigas.
Installation instructions via the wiki or through the eab thread.
